This invention relates to telecommunication equipment which terminates subscriber lines and supports high speed data services for subscribers. The invention is especially suited but not limited to providing high speed data services which exceed the capability of conventional POTS terminating equipment.
In the United States, subscribers are commonly provided with telephone services known as plain old telephone services (POTS). Such services include providing conventional dial tone and automated dialing features, including the use of dual frequency tone signaling to communicate dialed number information. Additional modem telephone features include conferencing, call waiting, incoming caller identification and other commercially available features.
Subscribers utilize a POTS line to carry conventional modem signals controlled by a personal computer to another modem via the public switch telephone network. Modems are currently available which support data communication rates up to 56 Kilobits per second (Kbps) over dial up analog subscriber lines. Those skilled in the art will understand that the maximum data rate which can be transmitted using modems over a POTS subscriber line is limited by the sampling rate, the band width of the channel, and the rate by which the analog signals are converted to digital signals by the line card units which terminate each POTS line at a central office. Thus, conventional modem data rates are limited by POTS line cards which terminate the subscriber lines.
Subscribers in the United States can lease special subscriber lines from their telephone service providers which accommodate higher data rates than are supported by conventional dial up subscriber lines. Such higher speed lines utilize different terminating circuitry at the central office to accommodate higher data rates. For example, integrated service digital network (ISDN) terminating equipment will provide a subscriber with a capability of higher data rates than a conventional POTS terminated line. For example, a known asynchronous digital subscriber line (ADSL) technique which is supported by available equipment provides a significantly higher data rate to a subscriber over a conventional copper two-wire subscriber line. Of course, the ADSL service requires proper terminating equipment at the central office and at the consumer premises to accommodate the greater throughput capabilities, i.e. data rates.
FIG. 1 illustrates some available services in the United States to subscribers using conventional two-wire copper loops. Equipment to the right of the dashed line 100 represents customer premise equipment (CPE). Equipment to the left of the dashed line 100 represents central office line termination equipment. A POTS line interface 102, also known as a line card, provides an interface between digital incoming and outgoing communication lines 104 and 106, and analog signals carried on subscriber line 108. For example, communication lines 104 and 106 may carry 64 Kb per second pulse coded modulation (PCM) signals representative of analog information received from and transmitted to line 108. A main distribution frame (MDF) 110 is used to interconnect a plurality of incoming subscriber lines to various terminating equipment at the central office. In this example, a line 108 is connected through a POTS splitter 112 and the MDF 110 to a subscriber line 114. A conventional telephone instrument 116 at the consumer's premise is connected through a POTS splitter 118 to the subscriber line 114.
FIG. 1 also illustrations another service to the subscriber which provides high speed data capability. An ADSL interface circuit 120 provides an interface between the central office and the subscriber for terminating the received data at rates up to several megabits per second (Mbps). Lines 122 and 124 provide inbound and outbound digital data communications, representative of information to and from the subscriber, carried on line 126. Line 126 is connected via the POTS splitter 112 and the MDF 110 to the subscriber line 114. An ADSL interface 128 provides an interface between conventional digital data, communicated with a subscriber's personal computer 130, and ADSL analog format signaling communicated on a line 132. The POTS splitter 118 couples the ADSL signal between the ADSL interface 128 and the subscriber line 114. The advantage to the user is that the ADSL facilities support a substantially higher-data rate than would be available if the subscriber utilized communications terminated via the POTS line interface 102.
A disadvantage of the system shown in FIG. 1 is that there is one ADSL interface 120 corresponding to each personal computer 130. Additionally, as the number of ADSL subscribers increases, the number of ADSL interfaces connected to the subscriber lines, such as subscriber line 114, must also increase. However, most ADSL service subscribers do not use ADSL services continuously. Thus, the ADSL interfaces 120 will be idle a significant amount of time. At the present, ADSL interface circuitry is expensive. This problem is magnified as more and more subscribers request ADSL service. Therefore, there is a need to provide high speed services, such as ADSL, while minimizing the cost of implementing the services.